Characteristics and Mechanisms of Persistent High Temperature in Hefei during the Summer of 2022

A rare persistent high temperature event occurred in Hefei in summer 2022, which caused serious impacts on many sectors. Therefore, analyzing the causes of the abnormal high temperature event is of great significance for improving the climate projection in the flood season. Based on the ground observation data of 1961－2022 and reanalysis data from NCEP/NCAR, the spatiotemporal evolution characteristics of the high temperature and drought event in Hefei are analyzed. Meanwhile, by comparing the typical circulation fields of historical high temperature processes with that of the extreme high temperature process in 2022, we discuss the possible causes of the persistent high temperature event in 2022 from the perspective of atmospheric circulation anomaly and SST forcing. The results show that: (1) The summer of 2022 in Hefei has experienced an extreme high temperature process that was of long duration, the highest average temperature in history, the highest number of high temperature days in history, and unusually less precipitation. The period from 1 to 22 August was the most prominent period of high temperature and low precipitation. (2) The temperature in Hefei has entered a warmer period since the 1990s and changed abruptly in the summer of 2008. (3) A blocking situation was identified to the west of the Ural mountains, with a trough of low pressure over the West Siberia. The troposphere in East Asia, including Hefei, was controlled by an anomalous anticyclone. This 'negative-positive-negative' pattern of meridional wave trains structure in the middle and high latitudes of the Northern Hemisphere is a typical circulation configuration for the historical high temperature process in Hefei. (4) The direct causes of the extreme high temperature process were the anomalous West Pacific subtropical high, which was found to be with enhanced intensity, larger coverage and westward movement, and the South Asia high, which extended abnormally eastward. The stable circulation situation, the weak cold air force, the northward water vapor transport, and the abnormally strong vertical sinking movement all contributed to the development and enhancement of this high temperature process. (5) The persistent La Ni?a event caused tropical sea temperature anomalies, which in turn led to the significant enhancement of the Walker and Hadley circulations. There was a significant abnormal sinking movement near 25°－35°N, which caused a stable westward extension of the West Pacific subtropical high, resulting in the occurrence of the extreme high temperature event.